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DDE Was Detected in All 60 Spanish Birds; Red Kites Had the Highest Medians for Most Pollutants

Red Kite in flight in Madrid, Spain
Research · Other research

A study published in 2026 found persistent organochlorine compounds and polychlorinated biphenyls (PCBs) in liver samples from three wild bird species collected in Extremadura, Spain. Persistent organic pollutants resist degradation and can remain in the environment and accumulate in biological tissues for long periods. Researchers analysed 20 white storks (Ciconia ciconia), 20 red kites (Milvus milvus) and 20 griffon vultures (Gyps fulvus). The birds had been found dead in the wild and submitted for necropsy. When poisoning was suspected, liver samples were sent for toxicological analysis.

The study’s primary aim was to adapt and validate a QuEChERS method for 19 persistent organic pollutants — 11 organochlorine compounds and eight PCBs — in lipid-rich bird liver. QuEChERS is a multi-residue extraction and clean-up approach designed to isolate many contaminants efficiently from the same sample. Here, the researchers modified the clean-up for liver tissue and then identified the compounds with gas chromatography–mass spectrometry. When the method was applied to the 60 wild-bird samples, an average of 11 compounds was detected above the method’s detection threshold in each liver. DDE, a persistent breakdown product of DDT, occurred in all 60 birds.

Red Kites Had the Highest Median for Most Compounds

Concentrations varied widely and included extreme values, so the researchers used medians for the species comparisons because a median is less strongly pulled by unusually high individual measurements. Red kites had the highest median concentration for every measured compound except β-HCH, which was highest in griffon vultures, DDD, which was highest in white storks, and PCB28, which was highest in griffon vultures.

Not every apparent difference was statistically supported. White storks and red kites differed for DDE, DDD, PCB153, PCB138 and PCB180. White storks and griffon vultures differed for α-HCH, heptachlor epoxide and PCB153. Red kites and griffon vultures differed for heptachlor epoxide, DDE, PCB118, PCB153, PCB138 and PCB180. The pattern therefore depended on the compound rather than forming one simple ranking across all pollutants.

Trophic Level Alone Did Not Explain the Pattern

Although red kites generally showed higher contamination than the other two species, the authors found no clear accumulation pattern that followed trophic level alone. They point instead to a combination of exposure, the chemical properties of each pollutant and species-specific physiology. In particular, DDE’s high stability and resistance to degradation help explain why it was so widespread, while more highly chlorinated PCB compounds are harder to metabolise and eliminate and therefore tend to persist in tissues.

The authors present the modified method as a practical tool for wildlife biomonitoring as well as a way to document continuing legacy contamination. Birds, especially raptors, can act as sentinels of environmental pollution, and the Extremadura samples illustrate the continuing legacy of historical contamination across very different wild-bird species.

Sources and image credit

  1. Ibáñez-Pernía, Y., Pérez-López, M., Fernández-Casado, D., & Soler-Rodríguez, F. (2026). Modified QuEChERS methodology for the analysis of OCs and PCBs in liver and its application in wild birds (white stork, red kite, and griffon vulture). Frontiers in Veterinary Science, 13, 1843311. https://doi.org/10.3389/fvets.2026.1843311Primary open-access research article published 12 June 2026. The method was applied to liver samples from 20 white storks, 20 red kites and 20 griffon vultures collected in Extremadura; an average of 11 persistent pollutants was detected per sample, DDE occurred in all samples, and red kites had the highest median concentrations for most measured compounds.

Image: Javier Perez Montes / Wikimedia Commons — red kite in flight in Madrid, Spain, 27 October 2024; cropped to 16:9. Representative image for this story; not presented as an animal or scene from the reported study or event. · CC BY-SA 4.0 · Source

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